1. Field of the Invention
The present invention relates to a process for the preparation of 1-chloro-2-trifluoromethyl-3,3,3-trifluoropropene [(CF.sub.3).sub.2 C .dbd. CHCl] from isobutylene, and, more especially, relates to the preparation of 1-chloro-2-trifluoromethyl-3,3,3-trifluoropropene by the catalytic chlorofluorination of isobutylene.
2. Description of the Prior Art:
1-Chloro-2-trifluoromethyl-3,3,3-trifluoropropene is a known compound. This olefin is of value as an intermediate in the preparation of hexafluoroisobutylene. Hexafluoroisobutylene, i.e., 3,3,3-trifluoro-2-trifluoromethyl-1-propene, is a valuable commercial monomer used in the production of a number of polymeric materials. Among such polymers is the copolymer with vinylidene fluoride, the preparation of which is described in U.S. Pat. No. 3,706,723 to Cnandrasekeran et al. Hexafluoroisobutylene is presently advantageously prepared from hexafluoroacetone and ketene. See U.S. Pat. No. 3,894,097 to Vanderkooi, Jr., et al. The high costs and limited availability of hexafluoroacetone nevertheless militate against the use of this route for manufacturing commercial quantities of hexafluoroisobutylene. Alternate routes to the preparation of hexafluoroisobutylene are, for example, disclosed or noted in the aforesaid '097 Vanderkooi, Jr. et al patent, as well as in the U.S. Pat. No. 3,655,786 to Gilbert et al.
The known 1-chloro-2-trifluoromethyl-3,3,3-trifluoropropene has itself been prepared by the chlorofluorination of isobutylene in the presence of elemental carbon. Compare British Patent Specification No. 1,087,873. Isobutylene has also been non-catalytically chlorofluorinated in an empty tube, as per Canadian Pat. No. 942,323 and U.S. Pat. No. 3,436,430 to Hall. Nonetheless, the procedures disclosed in these patents are unsatisfactory because the yields of product 1-chloro-2-trifluoromethyl-3,3,3-trifluoropropene are low and, for that matter, conducting the procedures outlined at examples 1 and 2 of the '873 British patent even gives rise to concomitant, massive breakdown to halomethanes.